Systems and methods for supplying auxiliary fuel streams during intermittent byproduct discharge from pressure swing adsorption assemblies

ABSTRACT

Combustion fuel stream supply systems for use with pressure swing adsorption (PSA) assemblies, and hydrogen-generation assemblies and/or fuel cell systems containing the same. The PSA assemblies are operated according to a PSA cycle to receive a mixed gas stream and, while producing a product hydrogen stream therefrom, intermittently discharge a byproduct stream. The byproduct stream, when available, may be delivered as a fuel stream to a heating assembly, which may heat the hydrogen-producing region that produces the mixed gas stream. A combustion fuel stream supply system selectively supplies an auxiliary fuel stream when a byproduct stream is not discharged or otherwise does not have a predetermined combustion fuel value sufficient, when combusted, to maintain the hydrogen-producing region within a desired temperature range. The one or more streams supplied to the heating assembly have a combined combustion fuel value at least as great as the predetermined threshold value.

FIELD OF THE DISCLOSURE

The present disclosure is directed generally to hydrogen-generationassemblies that include pressure swing adsorption assemblies, and moreparticularly to systems and methods for providing a heating assemblywith a continuous flow of combustible fuel, having a fuel value at leastas great as a predetermined threshold fuel value, that is sufficient,when combusted, to maintain a selected component of thehydrogen-generation assembly at or within a desired temperature range.

BACKGROUND OF THE DISCLOSURE

A hydrogen-generation assembly is an assembly that includes a fuelprocessing system that is adapted to convert one or more feedstocks intoa product stream containing hydrogen gas as a majority component. Theproduced hydrogen gas may be used in a variety of applications. One suchapplication is energy production, such as in electrochemical fuel cells.An electrochemical fuel cell is a device that converts a fuel and anoxidant to electricity, a reaction product, and heat. For example, fuelcells may convert hydrogen and oxygen into water and electricity. Insuch fuel cells, the hydrogen is the fuel, the oxygen is the oxidant,and the water is the reaction product. Fuel cells typically require highpurity hydrogen gas to prevent the fuel cells from being damaged duringuse. The product stream from the fuel processing system of ahydrogen-generation assembly may contain impurities, illustrativeexamples of which include one or more of carbon monoxide, carbondioxide, methane, unreacted feedstock, and water. Therefore, there is aneed in many conventional fuel cell systems to include suitablestructure for removing impurities from the impure hydrogen streamproduced in the fuel processing system and/or from thehydrogen-containing fuel stream for a fuel cell stack.

A pressure swing adsorption (PSA) process is an example of a mechanismthat may be used to remove impurities from an impure hydrogen gas streamby selective adsorption of one or more of the impurities present in theimpure hydrogen stream. The adsorbed impurities can be subsequentlydesorbed and removed from the PSA assembly. PSA is a pressure-drivenseparation process that typically utilizes a plurality of adsorbentbeds. The beds are cycled through a series of steps, such aspressurization, separation (adsorption), depressurization (desorption),and purge steps to selectively remove impurities from the hydrogen gasand then desorb the impurities.

Many hydrogen-generation assemblies include a heating assembly thatcombusts at least one fuel stream with air to produce a heated exhauststream for heating at least a portion of the hydrogen-generationassembly. The fuel streams may come from a variety of sources, includingthe PSA assembly. However, PSA assemblies are operated in PSA cyclesthat may result in the production of exhaust, or byproduct, streamshaving varying and intermittent flows and/or varying fuel values, oronly intermittently discharge byproduct streams. When used as a fuelstream for a heating assembly, this intermittency, variation, and/orinterruption in flow rate and/or fuel value may produce inconsistent,often unpredictable, results in the heating assembly, such as duringperiods of no fuel, periods of insufficient fuel, periods in which thefuel streams have variable fuel values, etc. As a result, it may bedifficult for the heating assembly to maintain a selected component ofthe hydrogen-generation assembly at a desired temperature or within adesired, or selected, temperature range. Similarly, at times, the PSAassembly may not be producing sufficient, or any, exhaust stream tomaintain a flame or other ignition source of a heating assembly inoperation.

SUMMARY OF THE DISCLOSURE

The present disclosure is directed to combustion fuel stream supplysystems for use with PSA assemblies, as well as to hydrogen-generationassemblies and/or fuel cell systems containing the same, and to methodsof operating the same. The PSA assemblies include at least one adsorbentbed, and typically a plurality of adsorbent beds, that include anadsorbent region including adsorbent adapted to remove impurities from amixed gas stream containing hydrogen gas as a majority component andother gases. The mixed gas stream may be produced by ahydrogen-producing region of a fuel processing system, and the PSAassembly may produce a product hydrogen stream that is consumed by afuel cell stack to provide a fuel cell system that produces electricalpower. The PSA assembly produces and intermittently discharges abyproduct stream containing impurities removed from the mixed gas streamand a purge gas, which may be or include hydrogen gas, and a heatingassembly may be adapted to receive the discharged byproduct stream as afuel stream for generating a heated exhaust stream. The heated exhauststream may be adapted to heat at least the hydrogen-producing region ofa fuel processing system, such as to maintain the region at a suitabletemperature or within a suitable temperature range for producing themixed gas stream.

The PSA assembly is adapted to cycle through at least one reducedbyproduct period, such as an equalization step of a PSA cycle, duringwhich a byproduct stream is not discharged or otherwise does not have acombustible fuel value sufficient, when combusted, to maintain thehydrogen-producing region within a desired temperature range. Acombustion fuel stream supply system is adapted to selectively supply,during at least a reduced byproduct period, an auxiliary fuel stream tothe heating assembly, such that the one or more streams supplied to theheating assembly have a combined combustion fuel value at least as greatas the corresponding, predetermined threshold value.

In some embodiments, the combustion fuel stream supply system includes areservoir assembly adapted to receive and store one or more fuel streamsfor reuse as an auxiliary fuel stream, or as a component thereof. Forexample, the combustion fuel stream supply system may be adapted toselectively direct at least a portion of the byproduct stream dischargedfrom the PSA assembly, having at least a predetermined threshold fuelvalue, to the reservoir assembly, and to selectively use at least aportion of the stored byproduct stream when supplying the auxiliary fuelstream. In this and other examples, the auxiliary fuel stream mayconsist solely of the stored byproduct stream, or the stored byproductstream may be combined with other fuel streams to form the auxiliaryfuel stream.

In some embodiments, the combustion fuel stream supply system is adaptedto selectively redirect at least a portion of the mixed gas stream priorto its delivery to the PSA assembly, and to use at least a portion ofthe redirected mixed gas stream as a “slip” stream when supplying theauxiliary fuel stream. In this and other examples, the auxiliary fuelstream may consist solely of the redirected mixed gas stream, or theredirected mixed gas stream may be combined with one or more other fuelstreams to form the auxiliary fuel stream.

Some embodiments may combine the above examples to provide an auxiliaryfuel stream that consists of more than one fuel stream. For example, anauxiliary fuel stream may include one or more stored gas streams (suchas a stored byproduct stream) in combination with one or more slipstreams (such as a redirected mixed gas stream). In the aforementionedembodiments, the combustion fuel supply system includes suitablemechanism(s) and structure for selectively supplying one or more streamsto the heating assembly to ensure a continuous supply of combustiblefuel having at least a predetermined threshold fuel value over a desiredoperational period. For example, some embodiments include devices toregulate flow of the various gas streams and sensors to monitor the fuelof various gas streams. Some embodiments further include a controlleradapted to determine which fuel stream(s) to supply as an auxiliary fuelstream, based at least in part on the monitored fuel values of thevarious fuel streams and/or the byproduct stream when discharged fromthe PSA assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an illustrative example of an energyproducing and consuming assembly that includes a hydrogen-generationassembly with an associated feedstock delivery system and a fuelprocessing system, as well as a fuel cell stack, and an optionalenergy-consuming device.

FIG. 2 is a schematic view of a hydrogen-producing assembly in the formof a steam reformer adapted to produce a reformate stream containinghydrogen gas and other gases from water and at least onecarbon-containing feedstock.

FIG. 3 is a schematic view of a fuel cell, such as may form part of afuel cell stack used with a hydrogen-generation assembly according tothe present disclosure.

FIG. 4 is a schematic view of a PSA assembly that may be used accordingto the present disclosure.

FIG. 5 is a schematic cross-sectional view of an adsorbent bed that maybe used with PSA assemblies according to the present disclosure.

FIG. 6 is a schematic cross-sectional view of another adsorbent bed thatmay be used with PSA assemblies according to the present disclosure.

FIG. 7 is a schematic cross-sectional view of another adsorbent bed thatmay be used with PSA assemblies according to the present disclosure.

FIG. 8 is a schematic cross-sectional view of the adsorbent bed of FIG.6 with a mass transfer zone being schematically indicated.

FIG. 9 is a schematic cross-sectional view of the adsorbent bed of FIG.8 with the mass transfer zone moved along the adsorbent region of thebed toward a distal, or product, end of the adsorbent region.

FIG. 10 is a schematic view of a combustion fuel stream supply systemsuitable for use with the hydrogen-producing assembly of FIG. 2.

DETAILED DESCRIPTION AND BEST MODE OF THE DISCLOSURE

FIG. 1 illustrates schematically an example of an energy producing andconsuming assembly 56. The energy producing and consuming assembly 56includes an energy-producing system 22 and at least one energy-consumingdevice 52 adapted to exert an applied load on the energy-producingsystem 22. In the illustrated example, the energy-producing system 22includes a fuel cell stack 24 and a hydrogen-generation assembly 46.More than one of any of the illustrated components may be used withoutdeparting from the scope of the present disclosure. The energy-producingsystem may include additional components that are not specificallyillustrated in the schematic figures, such as air delivery systems, heatexchangers, sensors, controllers, flow-regulating devices, fuel and/orfeedstock delivery assemblies, heating assemblies, cooling assemblies,and the like. System 22 may also be referred to as a fuel cell system.

As discussed in more detail herein, hydrogen-generation assembliesand/or fuel cell systems according to the present disclosure include aseparation assembly that includes at least one pressure swing adsorption(PSA) assembly that is adapted to increase the purity of the hydrogengas that is produced in the hydrogen-generation assembly and/or consumedin the fuel cell stack. In a PSA process, gaseous impurities are removedfrom a stream containing hydrogen gas. PSA is based on the principlethat certain gases, under the proper conditions of temperature andpressure, will be adsorbed onto an adsorbent material more strongly thanother gases. These impurities may thereafter be desorbed and removed,such as in the form of a byproduct stream. The success of using PSA forhydrogen purification is due to the relatively strong adsorption ofcommon impurity gases (such as, but not limited to, CO, CO₂,hydrocarbons including CH₄, and N₂) on the adsorbent material. Hydrogengas adsorbs only very weakly and so hydrogen passes through theadsorbent bed while the impurities are retained on the adsorbentmaterial.

As discussed in more detail herein, a PSA process typically involvesrepeated, or cyclical, application of at least pressurization,separation (adsorption), depressurization (desorption), and purge steps,or processes, to selectively remove impurities from the hydrogen gas andthen desorb the impurities. Accordingly, the PSA process may bedescribed as being adapted to repeatedly enable a PSA cycle of steps, orstages, such as the above-described steps. The degree of separation isaffected by the pressure difference between the pressure of the mixedgas stream and the pressure of the byproduct stream. Accordingly, thedesorption step will typically include reducing the pressure within theportion of the PSA assembly containing the adsorbed gases, andoptionally may even include drawing a vacuum (i.e., reducing thepressure to less than atmospheric or ambient pressure) on that portionof the assembly. Similarly, increasing the feed pressure of the mixedgas stream to the adsorbent regions of the PSA assembly may beneficiallyaffect the degree of separation during the adsorption step. Usingmultiple adsorbent regions, such as two or more adsorbent beds that arepressurized and depressurized in a reciprocal relationship, may permitpressure equalization between adsorbent beds, such as during one or moreequalization steps in which the beds are fluidly connected to partiallypressurize one bed by reducing the pressure in the other.

As illustrated schematically in FIG. 1, the hydrogen-generation assembly46 includes at least a fuel processing system 64 and a feedstockdelivery system 58, as well as the associated fluid conduitsinterconnecting various components of the system. As used herein, theterm “hydrogen-generation assembly” may be used to refer to the fuelprocessing system 64 and associated components of the energy-producingsystem, such as feedstock delivery systems 58, heating assemblies,separation regions or devices, air delivery systems, fuel deliverysystems, fluid conduits, heat exchangers, cooling assemblies, sensorassemblies, flow regulators, controllers, etc. All of these illustrativecomponents are not required to be included in any hydrogen-generationassembly or used with any fuel processing system according to thepresent disclosure. Similarly, other components may be included or usedas part of the hydrogen-generation assembly.

Regardless of its construction or components, the feedstock deliverysystem 58 is adapted to deliver to the fuel processing system 64 one ormore feedstocks via one or more streams, which may be referred togenerally as feedstock supply stream(s) 68. In the following discussion,reference may be made only to a single feedstock supply stream, but iswithin the scope of the present disclosure that two or more suchstreams, of the same or different composition, may be used. In someembodiments, air may be supplied to the fuel processing system 64 via ablower, fan, compressor or other suitable air delivery system, and/or awater stream may be delivered from a separate water source.

Fuel processing system 64 includes any suitable device(s) and/orstructure(s) that are configured to produce hydrogen gas as a majorityreaction product from the feedstock supply stream(s) 68. Asschematically illustrated in FIG. 1, the fuel processing system 64includes a hydrogen-producing region 70. Accordingly, fuel processingsystem 64 may be described as including a hydrogen-producing region 70that produces a hydrogen-rich stream 74 that includes hydrogen gas as amajority component from the feedstock supply stream. While stream 74contains hydrogen gas as its majority component, it also contains othergases, and as such may be referred to as a mixed gas stream, whichcontains hydrogen gas and other gases. Illustrative, non-exclusiveexamples of these other gases, or impurities, include one or more ofsuch illustrative impurities as carbon monoxide, carbon dioxide, water,methane, and unreacted feedstock.

Illustrative examples of suitable mechanisms for producing hydrogen gasfrom feedstock supply stream 68 include steam reforming and autothermalreforming, in which reforming catalysts are used to produce hydrogen gasfrom a feedstock supply stream 68 containing water and at least onecarbon-containing feedstock. Other examples of suitable mechanisms forproducing hydrogen gas include pyrolysis and catalytic partial oxidationof a carbon-containing feedstock, in which case the feedstock supplystream 68 does not contain water. Still another suitable mechanism forproducing hydrogen gas is electrolysis, in which case the feedstock iswater. Illustrative examples of suitable carbon-containing feedstocksinclude at least one hydrocarbon or alcohol. Illustrative examples ofsuitable hydrocarbons include methane, propane, natural gas, diesel,kerosene, gasoline and the like. Illustrative examples of suitablealcohols include methanol, ethanol, and polyols, such as ethylene glycoland propylene glycol.

The hydrogen-generation assembly 46 may utilize more than a singlehydrogen-producing mechanism in the hydrogen-producing region 70 and mayinclude more than one hydrogen-producing region. Each of thesemechanisms is driven by, and results in, different thermodynamicbalances in the hydrogen-generation assembly 46. Accordingly, thehydrogen-generation assembly 46 may further include a temperaturemodulating assembly 71, such as a heating assembly and/or a coolingassembly. The temperature modulating assembly 71 may be configured aspart of the fuel processing system 64 or may be an external componentthat is in thermal and/or fluid communication with thehydrogen-producing region 70. The temperature modulating assembly 71 mayconsume a fuel stream, such as to generate heat. While not required inall embodiments of the present disclosure, the fuel stream may bedelivered from the feedstock delivery system. For example, and asindicated in dashed lines in FIG. 1, this fuel, or feedstock, may bereceived from feedstock delivery system 58 via a fuel supply stream 69.The fuel stream 69 may include combustible fuel, fluids to facilitatecooling, and/or any fluid appropriate for the temperature modulatingassembly 71. In some embodiments, the temperature modulating assemblymay receive some or all of its feedstock from other sources or supplystreams, such as from additional storage tanks, a combustion fuel streamsupply system, and so forth. It may also receive an air stream from anysuitable source, including the environment within which the assembly isused. Blowers, fans and/or compressors may be used to provide the airstream, but this is not required to all embodiments.

The temperature modulating assembly 71 may include one or more heatexchangers, burners, combustion systems, and other such devices forsupplying heat to regions of the fuel processing system and/or otherportions of assembly 56. Depending on the configuration of thehydrogen-generation assembly 46, the temperature modulating assembly 71may also, or alternatively, include heat exchangers, fans, blowers,cooling systems, and other such devices for cooling regions of the fuelprocessing system 64 or other portions of assembly 56. For example, whenthe fuel processing system 64 is configured with a hydrogen-producingregion 70 based on steam reforming or another endothermic reaction, thetemperature modulating assembly 71 may include systems for supplyingheat to maintain the temperature of the hydrogen-producing region 70 andthe other components in the proper range.

When the fuel processing system is configured with a hydrogen-producingregion 70 based on catalytic partial oxidation or another exothermicreaction, the temperature modulating assembly 71 may include systems forremoving heat, i.e., supplying cooling, to maintain the temperature ofthe fuel processing system in the proper range. As used herein, the term“heating assembly” is used to refer generally to temperature modulatingassemblies that are configured to supply heat or otherwise increase thetemperature of all or selected regions of the fuel processing system. Asused herein, the term “cooling assembly” is used to refer generally totemperature moderating assemblies that are configured to cool, or reducethe temperature of, all or selected regions of the fuel processingsystem.

In FIG. 2, an illustrative example of a hydrogen-generation assembly 46that includes fuel processing system 64 with a hydrogen-producing region70 that is adapted to produce mixed gas stream 74 by steam reforming oneor more feedstock supply streams 68 containing water 80 and at least onecarbon-containing feedstock 82. As illustrated, region 70 includes atleast one reforming catalyst bed 84 containing one or more suitablereforming catalysts 86. In the illustrative example, thehydrogen-producing region may be referred to as a reforming region, andthe mixed gas stream may be referred to as a reformate stream.

As also shown in FIGS. 1 and 2, the mixed gas stream is adapted to bedelivered to a separation region, or assembly, 72 which includes atleast one PSA assembly 73. PSA assembly 73 separates the mixed gas (orreformate) stream into product hydrogen stream 42 and at least onebyproduct stream 76 that contains at least a substantial portion of theimpurities, or other gases, present in mixed gas stream 74. Byproductstream 76 may contain no hydrogen gas, but it typically will containsome hydrogen gas. While not required, it is within the scope of thepresent disclosure that fuel processing system 64 may be adapted toproduce one or more byproduct streams containing sufficient amounts ofhydrogen (and/or other) gas(es) to be suitable for use as a fuel, orfeedstock, stream for a heating assembly for the fuel processing system.In some embodiments, the byproduct stream may have sufficient fuel valueto enable the heating assembly, when present, to maintain thehydrogen-producing region at a desired operating temperature or within aselected range of temperatures.

As illustrated in FIG. 2, the hydrogen-generation assembly includes atemperature modulating assembly in the form of a heating assembly 71that is adapted to produce a heated exhaust stream 88 that in turn isadapted to heat at least the reforming region of the hydrogen-generationassembly. It is within the scope of the present disclosure that stream88 may be used to heat other portions of the hydrogen-generationassembly and/or energy-producing system 22.

As indicated in dashed lines in FIG. 2 (and FIG. 1), it is within thescope of the present disclosure that the byproduct stream from the PSAassembly may form at least a portion of the fuel stream for the heatingassembly. Also shown in FIG. 2 are air stream 90, which may be deliveredfrom any suitable air source, and fuel stream 92, which contains anycombustible fuel (or fuels) suitable for being combusted with air in theheating assembly, such as byproduct stream 76, or a portion thereof.

The term “fuel value,” as used herein, refers to the hydrogen and/orother combustible gas content of a gas stream, and/or other measurablecharacteristics of the gas stream, such as flow rate, chemicalcomposition, and so forth, which individually or collectively relate tothe suitability of the gas stream, relative to the configuration of theheating assembly, for being combusted (with air, in some embodiments) toproduce a heated exhaust stream adapted to heat a selected component ofthe hydrogen-generation assembly (the hydrogen-producing region, in someembodiments), for example, to maintain the heated component within apredetermined temperature range for producing a mixed gas stream.

As an illustrative, non-limiting example, a byproduct stream that ishighly combustible may have a low fuel value if its flow rate isinsufficient, when the stream is combusted in the heating assembly, toproduce a suitable heated exhaust stream. This example may describe abyproduct stream that has a minimal, or even a zero, flow rate. Asexplained in more detail below, operation of a PSA assembly is usuallycyclic in nature, and may produce and/or discharge a byproduct streamonly intermittently during each cycle. During periods in which thebyproduct stream is not produced, the stream may be said to have a lowfuel value because it is not present (i.e., has minimal or zero flowrate). In some embodiments, operation of a PSA assembly that has two (ormore) adsorbent beds may include one or more equalization steps thatinvolve temporarily interconnecting two beds in order to equalize thepressure in the beds. During such an equalization step, little or nobyproduct stream may be exhausted or discharged from a PSA assembly, andthe exhausted byproduct stream may be said to have a low fuel value,either because it is not present or is being redirected within the PSAassembly (i.e., by temporarily flowing from one adsorbent bed to theother).

Conversely, a byproduct stream with a comparatively high flow rate mayhave a low fuel value if the combustible gas component of the stream isinsufficient to produce a suitable heated exhaust stream (including gasstreams having minimal or even no combustible gas component).

The fuel value of a fuel stream may be variable, such as if a fuelstream has a variable or discontinuous flow rate, fluctuates in itslevel of combustible fuel content, and so forth. In other words,depending on the nature of the fuel stream, its fuel value may, over agiven time increment, fluctuate between being lower than a particular orpredetermined fuel value and being greater than the fuel value. Thepredetermined fuel value may be the fuel value sufficient to produce aheated exhaust stream capable of maintaining the hydrogen-producingregion in a predetermined temperature range, also referred to herein asa “threshold fuel value,” or may be some other fuel value.

As an illustrative example of temperatures that may be achieved and/ormaintained in hydrogen-producing region 70 through the use of heatingassembly 71, steam reformers typically operate at temperatures in therange of 200° C. and 900° C. Temperatures outside of this range arewithin the scope of the disclosure. When the carbon-containing feedstockis methanol, the steam reforming reaction will typically operate in atemperature range of approximately 200-500° C. Illustrative subsets ofthis range include 350-450° C., 375-425° C., and 375-400° C. When thecarbon-containing feedstock is a hydrocarbon, ethanol, or a similaralcohol, a temperature range of approximately 400-900° C. will typicallybe used for the steam reforming reaction. Illustrative subsets of thisrange include 750-850° C., 725-825° C., 650-750° C., 700-800° C.,700-900° C., 500-800° C., 400-600° C., and 600-800° C.

The temperature ranges discussed herein illustrate examples of suitabletemperature ranges for producing the mixed gas stream, and alsodemonstrate that the temperature range for a particular embodiment orembodiments may be based, at least in part, on the nature of thecarbon-containing feedstock.

Correspondingly, the threshold fuel value, or the fuel value of acombustible fuel stream suitable for combustion in a heating assemblythat is sufficient to produce a heated exhaust stream capable ofmaintaining the hydrogen-producing region in a predetermined temperaturerange, may vary, depending, for example, on the feedstock used. Otherfactors, such as the implemented structural configuration of the heatingassembly, its proximity to the hydrogen-producing region, and so forth,may also relate to the threshold fuel value for a particular embodiment,which may vary even within a particular embodiment. Considering suchfactors, one or more threshold fuel values may be predetermined for agiven embodiment.

The fluctuations in fuel value of a combustible fuel stream may beregular or irregular, and may vary among the fuel streams of aparticular embodiment. As noted above in the examples of a byproductstream, some fluctuations may be cyclical or periodic in nature: abyproduct stream exhausted from a PSA assembly may have a fuel valuelower than a predetermined threshold fuel value during an equalizationstep or when not being produced, even though the fuel value is at leastas great as the threshold fuel value at other times. The term “reducedbyproduct period” is used herein to describe operational periods whenthe heating assembly 71 is providing a heated exhaust stream to maintainthe hydrogen-producing region within a predetermined temperature rangesuitable for producing a mixed gas stream 74, during which the byproductstream from the PSA assembly has a fuel value lower than a predeterminedthreshold fuel value. As mentioned above, illustrative examples ofreduced byproduct periods include periods during which the byproductstream from the PSA assembly is being used for other purposes, or is notbeing generated, and so forth.

Returning to the illustrative embodiment shown in FIG. 2, fuel stream 92is supplied to the heating assembly via a combustion fuel stream supplysystem 140, which is adapted to fuel receive streams, such as byproductstream 76 and mixed gas stream 74, and deliver one or more fuel streams92 having a combined combustion fuel value at least as great as acorresponding, predetermined threshold value to the heating assembly.Combustion fuel stream supply system 140 may optionally receive anyother combustible fuel streams, such as the anode exhaust stream from afuel cell stack, one or more of the above-described carbon-containingfeedstocks from the feedstock delivery system, a product hydrogen streamfrom the PSA assembly, and so forth, as well as fuel streams fromstorage tanks and other sources. As explained in more detail herein,combustion fuel stream supply system 140 includes a delivery assembly142 adapted to collect the various combustible fuel streams andselectively deliver one or more fuel streams 92 to the heating assembly.Delivery assembly 142 may further include a reservoir assembly 144adapted to receive and store one or more combustible fuel streams foruse as all or part of a fuel stream 92.

Fuel stream 92 may therefore include one or more of the combustible fuelstreams, such as those listed above. For example, when the byproductstream from the PSA assembly 73 has a fuel value at least as great as apredetermined threshold fuel value, fuel stream 92 may include thebyproduct stream as its majority, or even as its only, component.Conversely, when the fuel value of the byproduct stream is lower thanthe threshold fuel value, the fuel stream 92 may include one or more ofthe other combustible streams listed above, exclusive of, or in additionto, the byproduct stream or a portion thereof. In this capacity, the oneor more other combustible streams may be referred to, eitherindividually or collectively, as an “auxiliary fuel stream.” As such,the combustion fuel stream supply system 140, at least in the embodimentillustrated in FIG. 2, is adapted to deliver a fuel stream 92, whichincludes either the byproduct stream and/or an auxiliary stream, to theheating assembly, such that the one or more streams supplied to theheating assembly have a combined fuel value at least as great as acorresponding, predetermined threshold value.

With continued reference to FIGS. 1 and 2, it is within the scope of thepresent disclosure that separation region 72 may be implemented withinsystem 22 anywhere downstream from the hydrogen-producing region, andupstream from the fuel cell stack. In the illustrative example shownschematically in FIG. 1, the separation region is depicted as part ofthe hydrogen-generation assembly, but this construction is not required.It is also within the scope of the present disclosure that thehydrogen-generation assembly may utilize a chemical or physicalseparation process in addition to PSA assembly 73 to remove or reducethe concentration of one or more selected impurities from the mixed gasstream. When separation assembly 72 utilizes a separation process inaddition to PSA, the one or more additional processes may be performedat any suitable location within system 22 and are not required to beimplemented with the PSA assembly. An illustrative chemical separationprocess is the use of a methanation catalyst to selectively reduce theconcentration of carbon monoxide present in stream 74. Otherillustrative chemical separation processes include partial oxidation ofcarbon monoxide to form carbon dioxide and water-gas shift reactions toproduce hydrogen gas and carbon dioxide from water and carbon monoxide.Illustrative physical separation processes include the use of a physicalmembrane or other barrier adapted to permit the hydrogen gas to flowtherethrough but adapted to prevent at least selected impurities frompassing therethrough. These membranes may be referred to as beinghydrogen-selective membranes. Illustrative examples of suitablemembranes are formed from palladium or a palladium alloy and aredisclosed in the references incorporated herein.

The hydrogen-generation assembly 46 preferably is adapted to produce atleast substantially pure hydrogen gas, and even more preferably, thehydrogen-generation assembly is adapted to produce pure hydrogen gas.For the purposes of the present disclosure, substantially pure hydrogengas is greater than 90% pure, preferably greater than 95% pure, morepreferably greater than 99% pure, and even more preferably greater than99.5% or even 99.9% pure. Illustrative, nonexclusive examples ofsuitable fuel processing systems are disclosed in U.S. Pat. Nos.6,221,117, 5,997,594, 5,861,137, and pending U.S. Patent ApplicationPublication No. 2001/0045061. The complete disclosures of theabove-identified patents are hereby incorporated by reference for allpurposes.

Hydrogen gas from fuel processing system 64 may be delivered to one ormore of the fuel cell stack 24, and/or a storage device 62, via producthydrogen stream 42. Some or all of hydrogen stream 42 may additionally,or alternatively, be delivered, via a suitable conduit, for use inanother hydrogen-consuming process, burned for fuel or heat, for exampleas part of an auxiliary stream supplied to the heating assembly forcombustion, or stored for later use. With reference to FIG. 1, thehydrogen gas used as a proton source, or reactant, for fuel cell stack24 may be delivered to the stack from one or more of fuel processingsystem 64 and storage device 62. Fuel cell stack 24 includes at leastone fuel cell 20, and typically includes a plurality of fluidly andelectrically interconnected fuel cells. When these cells are connectedtogether in series, the power output of the fuel cell stack is the sumof the power outputs of the individual cells. The cells in stack 24 maybe connected in series, parallel, or combinations of series and parallelconfigurations.

FIG. 3 illustrates schematically a fuel cell 20, one or more of whichmay be configured to form fuel cell stack 24. The fuel cell stacks ofthe present disclosure may utilize any suitable type of fuel cell, andpreferably fuel cells that receive hydrogen and oxygen as proton sourcesand oxidants. Illustrative examples of types of fuel cells includeproton exchange membrane (PEM) fuel cells, alkaline fuel cells, solidoxide fuel cells, molten carbonate fuel cells, phosphoric acid fuelcells, and the like. For the purpose of illustration, an example of afuel cell 20 in the form of a PEM fuel cell is schematically illustratedin FIG. 3.

Proton exchange membrane fuel cells typically utilize amembrane-electrode assembly 26 consisting of an ion exchange, orelectrolytic, membrane 28 located between an anode region 30 and acathode region 32. Each region 30 and 32 includes an electrode 34,namely an anode 36 and a cathode 38, respectively. Each region 30 and 32also includes a support 39, such as a supporting plate 40. Support 39may form a portion of a bipolar plate assembly between adjacent fuelcells. The supporting plates 40 of fuel cells 20 typically carry therelative voltage potentials produced by the fuel cells.

In operation, hydrogen gas from product stream 42 is delivered to theanode region, and oxidant 44 is delivered to the cathode region. Atypical, but not exclusive, oxidant is oxygen. As used herein, hydrogenrefers to hydrogen gas and oxygen refers to oxygen gas. The followingdiscussion will refer to hydrogen as the proton source, or fuel, for thefuel cell (stack), and oxygen as the oxidant, although it is within thescope of the present disclosure that other fuels and/or oxidants may beused. Hydrogen and oxygen 44 may be delivered to the respective regionsof the fuel cell via any suitable mechanism from respective sources 47and 48. Illustrative examples of suitable sources 48 of oxygen 44include a pressurized tank of oxygen or air, or a fan, compressor,blower or other device for directing air to the cathode region.

Hydrogen and oxygen typically combine with one another via anoxidation-reduction reaction. Although membrane 28 restricts the passageof a hydrogen molecule, it will permit a hydrogen ion (proton) to passthrough it, largely due to the ionic conductivity of the membrane. Thefree energy of the oxidation-reduction reaction drives the proton fromthe hydrogen gas through the ion exchange membrane. As membrane 28 alsotends not to be electrically conductive, an external circuit 50 is thelowest energy path for the remaining electron, and is schematicallyillustrated in FIG. 3. In cathode region 32, electrons from the externalcircuit and protons from the membrane combine with oxygen to producewater and heat.

Also shown in FIG. 3 are an anode purge, or exhaust, stream 54, whichmay contain hydrogen gas, and a cathode air exhaust stream 55, which istypically at least partially, if not substantially, depleted of oxygen.Fuel cell stack 24 may include a common hydrogen (or other reactant)feed, air intake, and stack purge and exhaust streams, and accordinglywill include suitable fluid conduits to deliver the associated streamsto, and collect the streams from, the individual fuel cells. Similarly,any suitable mechanism may be used for selectively purging the regions.

In practice, a fuel cell stack 24 will typically contain a plurality offuel cells with bipolar plate assemblies separating adjacentmembrane-electrode assemblies. The bipolar plate assemblies essentiallypermit the free electron to pass from the anode region of a first cellto the cathode region of the adjacent cell via the bipolar plateassembly, thereby establishing an electrical potential through thestack. This net flow of electrons produces an electric current that maybe used to satisfy an applied load, such as from at least one of anenergy-consuming device 52 and the energy-producing system 22.

For a constant output voltage, such as 12 volts or 24 volts, the outputpower may be determined by measuring the output current. FIG. 1schematically depicts that energy-producing system 22 may include atleast one energy-storage device 78. Device 78, when included, may beadapted to store at least a portion of the electrical output, or power,79 from the fuel cell stack 24. An illustrative example of a suitableenergy-storage device 78 is a battery, but others may be used.Energy-storage device 78 may additionally or alternatively be used topower the energy-producing system 22 during start-up of the system.

The at least one energy-consuming device 52 may be electrically coupledto the energy-producing system 22, such as to the fuel cell stack 24and/or one or more energy-storage devices 78 associated with the stack.Device 52 applies a load to the energy-producing system 22 and draws anelectric current from the system to satisfy the load. This load may bereferred to as an applied load, and may include thermal and/orelectrical load(s). It is within the scope of the present disclosurethat the applied load may be satisfied by the fuel cell stack, theenergy-storage device, or both the fuel cell stack and theenergy-storage device. Illustrative examples of devices 52 include motorvehicles, recreational vehicles, boats and other sea craft, and anycombination of one or more residences, commercial offices or buildings,neighborhoods, tools, lights and lighting assemblies, appliances,computers, industrial equipment, signaling and communications equipment,radios, electrically powered components on boats, recreational vehiclesor other vehicles, battery chargers and even the balance-of-plantelectrical requirements for the energy-producing system 22 of which fuelcell stack 24 forms a part. As indicated in dashed lines at 77 in FIG.1, the energy-producing system may, but is not required to, include atleast one power management module 77. Power management module 77includes any suitable structure for conditioning or otherwise regulatingthe electricity produced by the energy-producing system, such as fordelivery to energy-consuming device 52. Module 77 may include suchillustrative structure as buck or boost converters, inverters, powerfilters, and the like.

In FIG. 4, an illustrative example of a PSA assembly 73 is shown. PSAassembly 73 is shown to include a plurality of adsorbent beds 100 thatare fluidly connected via distribution assemblies 102 and 104. Beds 100may additionally or alternatively be referred to as adsorbent chambersor adsorption regions. The distribution assemblies have beenschematically illustrated in FIG. 4 and may include any suitablestructure for selectively establishing and restricting fluid flowbetween the beds and/or the input and output streams of assembly 73. Asshown, the input and output streams include at least mixed gas stream74, product hydrogen stream 42, and byproduct stream 76. Illustrativeexamples of suitable structures include one or more of manifolds, suchas distribution and collection manifolds that are respectively adaptedto distribute fluid to and collect fluid from the beds, and valves, suchas check valves, solenoid valves, purge valves, and the like. In theillustrative example, three beds 100 are shown, but it is within thescope of the present disclosure that the number of beds may vary, suchas to include more or fewer beds than shown in FIG. 4. Typically,assembly 73 will include at least two beds, and often will includethree, four, or more beds. While not required, assembly 73 is preferablyadapted to provide a continuous flow of product hydrogen stream, with atleast one of the plurality of beds exhausting this stream when theassembly is in use and receiving a continuous flow of mixed gas stream74.

In the illustrative example, distribution assembly 102 is adapted toselectively deliver mixed gas stream 74 to the plurality of beds and tocollect byproduct stream 76, for example to exhaust byproduct streamfrom the PSA assembly 73, or in some embodiments to selectively redirectat least a portion of the byproduct stream to another of the beds 100,for example during one or more equalization steps. Distribution assembly104 is adapted to collect the purified hydrogen gas that passes throughthe beds and which forms product hydrogen stream 42, and in someembodiments to deliver a portion of the purified hydrogen gas to thebeds for use as a purge stream. The distribution assemblies may beconfigured for fixed or rotary positioning relative to the beds.Furthermore, the distribution assemblies may include any suitable typeand number of structures and devices to selectively distribute,regulate, meter, prevent and/or collect flows of the corresponding gasstreams. As illustrative, non-exclusive examples, distribution assembly102 may include mixed gas and exhaust manifolds, or manifold assemblies,and distribution assembly 104 may include product and purge manifolds,or manifold assemblies. In practice, PSA assemblies that utilizedistribution assemblies that rotate relative to the beds may be referredto as rotary pressure swing adsorption assemblies, and PSA assemblies inwhich the manifolds and beds are not adapted to rotate relative to eachother to selectively establish and restrict fluid connections may bereferred to as fixed bed, or discrete bed, pressure swing adsorptionassemblies. Both constructions are within the scope of the presentdisclosure.

Gas purification by pressure swing adsorption involves sequentialpressure cycling and flow reversal of gas streams relative to theadsorbent beds. In the context of purifying a mixed gas stream comprisedsubstantially of hydrogen gas, the mixed gas stream is delivered underrelatively high pressure to one end of the adsorbent beds and therebyexposed to the adsorbent(s) contained in the adsorbent region thereof.Illustrative examples of delivery pressures for mixed gas stream 74include pressures in the range of 40-200 psi, such as pressures in therange of 50-150 psi, 50-100 psi, 100-150 psi, 70-100 psi, etc., althoughpressures outside of this range are within the scope of the presentdisclosure. As the mixed gas stream flows through the adsorbent region,carbon monoxide, carbon dioxide, water and/or other ones of theimpurities, or other gases, are adsorbed, and thereby at leasttemporarily retained, on the adsorbent. This is because these gases aremore readily adsorbed on the selected adsorbents used in the PSAassembly. The remaining portion of the mixed gas stream, which now mayperhaps more accurately be referred to as a purified hydrogen stream,passes through the bed and is exhausted from the other end of the bed.In this context, hydrogen gas may be described as being the less readilyadsorbed component, while carbon monoxide, carbon dioxide, etc. may bedescribed as the more readily adsorbed components of the mixed gasstream. The pressure of the product hydrogen stream is typically reducedprior to utilization of the gas by the fuel cell stack.

To remove the adsorbed gases, the flow of the mixed gas stream isstopped, the pressure in the bed is reduced, and the now desorbed gasesare exhausted from the bed and, typically, from the PSA assembly asbyproduct stream 76. The desorption step often includes selectivelydecreasing the pressure within the adsorbent region through thewithdrawal of gas, typically in a countercurrent direction relative tothe feed direction. This desorption step may also be referred to as adepressurization, or blowdown, step. This step often includes or isperformed in conjunction with the use of a purge gas stream, which istypically delivered in a countercurrent flow direction to the directionat which the mixed gas stream flows through the adsorbent region. Anillustrative example of a suitable purge gas stream is a portion of theproduct hydrogen stream, as this stream is comprised of hydrogen gas,which is less readily adsorbed than the adsorbed gases. Other gases maybe used in the purge gas stream, although these gases preferably areless readily adsorbed than the adsorbed gases, and even more preferablyare not adsorbed, or are only weakly adsorbed, on the adsorbent(s) beingused.

As discussed, this desorption step may include drawing an at leastpartial vacuum on the bed, but this is not required. While not required,it is often desirable to utilize one or more equalization steps, inwhich two or more beds are fluidly interconnected to permit the beds toequalize the relative pressures therebetween. For example, one or moreequalization steps may precede the desorption and pressurization steps.Prior to the desorption step, equalization is used to reduce thepressure in the bed and to recover some of the purified hydrogen gascontained in the bed, while prior to the (re)pressurization step,equalization is used to increase the pressure within the bed.Equalization may be accomplished using cocurrent and/or countercurrentflow of gas. After the desorption and/or purge step(s) of the desorbedgases is completed, the bed is again pressurized and ready to againreceive and remove impurities from the portion of the mixed gas streamdelivered thereto.

For example, when a bed is ready to be regenerated, it is typically at arelatively high pressure and contains a quantity of hydrogen gas. Whilethis gas (and pressure) may be removed simply by venting the bed, otherbeds in the assembly will need to be pressurized prior to being used topurify the portion of the mixed gas stream delivered thereto.Furthermore, the hydrogen gas in the bed to be regenerated preferably isrecovered so as to not negatively impact the efficiency of the PSAassembly. Therefore, interconnecting these beds in fluid communicationwith each other permits reduction of the pressure and hydrogen gas inthe bed to be regenerated while also increasing the pressure andhydrogen gas in a bed that will be used to purify impure hydrogen gas(i.e., mixed gas stream 74) that is delivered thereto.

As mentioned above, although gas flows between adsorbent beds that areinterconnected during an equalization step, little or no gas isexhausted from the PSA assembly. Instead, gas streams such as thepurified hydrogen gas streams, and/or those that include desorbed gases,are redirected within the PSA assembly during an equalization step. Morespecifically, for example, a purge or byproduct stream that includesdesorbed gases intended to be exhausted from the PSA assembly insteadmay flow between interconnected beds during an equalization step. Assuch, in embodiments in which the byproduct gas stream from the PSAassembly is used as a fuel stream for the heating assembly, anequalization step may result in a temporary interruption in the flow ofcombustible fuel.

Or, as expressed in terms as described above, an equalization step is anexample of a reduced byproduct period during which the byproduct streamhas a fuel value less than a predetermined threshold value sufficient toproduce a heated exhaust stream capable of maintaining thehydrogen-producing region in a predetermined temperature range. However,as explained in greater detail below, a combustion fuel stream supplysystem may be adapted, during reduced byproduct periods, to deliver anauxiliary fuel stream to the heating assembly.

In addition to, or in place of, one or more equalization steps, a bedthat will be used to purify the mixed gas stream may be pressurizedprior to the delivery of the mixed gas stream to the bed. For example,some of the purified hydrogen gas may be delivered to the bed topressurize the bed. While it is within the scope of the presentdisclosure to deliver this pressurization gas to either end of the bed,in some embodiments it may be desirable to deliver the pressurizationgas to the opposite end of the bed than to the end of the bed to whichthe mixed gas stream is delivered.

The above discussion of the general operation of a PSA assembly has beensomewhat simplified. Illustrative examples of pressure swing adsorptionassemblies, including components thereof and methods of operating thesame, are disclosed in U.S. Pat. Nos. 3,564,816, 3,986,849, 5,441,559,6,692,545, and 6,497,856, the complete disclosures of which are herebyincorporated by reference for all purposes.

In FIG. 5, an illustrative example of an adsorbent bed 100 isschematically illustrated. As shown, the bed defines an internalcompartment 110 that contains at least one adsorbent 112, with eachadsorbent being adapted to adsorb one or more of the components of themixed gas stream. It is within the scope of the present disclosure thatmore than one adsorbent may be used. For example, a bed may include morethan one adsorbent adapted to adsorb a particular component of the mixedgas stream, such as to adsorb carbon monoxide, and/or two or moreadsorbents that are each adapted to adsorb a different component of themixed gas stream. Similarly, an adsorbent may be adapted to adsorb twoor more components of the mixed gas stream. Illustrative examples ofsuitable adsorbents include activated carbon, alumina and zeoliteadsorbents. An additional example of an adsorbent that may be presentwithin the adsorbent region of the beds is a desiccant that is adaptedto adsorb water present in the mixed gas stream. Illustrative desiccantsinclude silica and alumina gels. When two or more adsorbents areutilized, they may be sequentially positioned (in a continuous ordiscontinuous relationship) within the bed or may be mixed together. Itshould be understood that the type, number, amount and form of adsorbentin a particular PSA assembly may vary, such as according to one or moreof the following factors: the operating conditions expected in the PSAassembly, the size of the adsorbent bed, the composition and/orproperties of the mixed gas stream, the desired application for theproduct hydrogen stream produced by the PSA assembly, the operatingenvironment in which the PSA assembly will be used, user preferences,etc.

When the PSA assembly includes a desiccant or other water-removalcomposition or device, it may be positioned to remove water from themixed gas stream prior to adsorption of other impurities from the mixedgas stream. One reason for this is that water may negatively affect theability of some adsorbents to adsorb other components of the mixed gasstream, such as carbon monoxide. An illustrative example of awater-removal device is a condenser, but others may be used between thehydrogen-producing region and adsorbent region, as schematicallyillustrated in dashed lines at 122 in FIG. 1. For example, at least oneheat exchanger, condenser or other suitable water-removal device may beused to cool the mixed gas stream prior to delivery of the stream to thePSA assembly. This cooling may condense some of the water present in themixed gas stream. Continuing this example, and to provide a morespecific illustration, mixed gas streams produced by steam reformerstend to contain at least 10%, and often at least 15% or more water whenexhausted from the hydrogen-producing (i.e., the reforming) region ofthe fuel processing system. These streams also tend to be fairly hot,such as having a temperature of at least 300° C. (in the case of manymixed gas streams produced from methanol or similar carbon-containingfeedstocks), and at least 600-800° C. (in the case of many mixed gasstreams produced from natural gas, propane or similar carbon-containingfeedstocks). When cooled prior to delivery to the PSA assembly, such asto an illustrative temperature in the range of 25-100° C. or even 40-80°C., most of this water will condense. The mixed gas stream may still besaturated with water, but the water content will tend to be less than 5wt %.

The adsorbent(s) may be present in the bed in any suitable form,illustrative examples of which include particulate form, bead form,porous discs or blocks, coated structures, laminated sheets, fabrics,and the like. When positioned for use in the beds, the adsorbents shouldprovide sufficient porosity and/or gas flow paths for the non-adsorbedportion of the mixed gas stream to flow through the bed withoutsignificant pressure drop through the bed. As used herein, the portionof a bed that contains adsorbent will be referred to as the adsorbentregion of the bed. In FIG. 5, an adsorbent region is indicated generallyat 114. Beds 100 also may (but are not required to) include partitions,supports, screens and other suitable structure for retaining theadsorbent and other components of the bed within the compartment, inselected positions relative to each other, in a desired degree ofcompression, etc. These devices are generally referred to as adsorbentsupports and are generally indicated in FIG. 5 at 116. Therefore, it iswithin the scope of the present disclosure that the adsorbent region maycorrespond to the entire internal compartment of the bed, or only asubset thereof. Similarly, the adsorbent region may be comprised of acontinuous region or two or more spaced apart regions without departingfrom the scope of the present disclosure.

In the illustrated example shown in FIG. 5, bed 100 includes at leastone port 118 associated with each end region of the bed. As indicated indashed lines, it is within the scope of the present disclosure thateither or both ends of the bed may include more than one port.Similarly, it is within the scope of the disclosure that the ports mayextend laterally from the beds or otherwise have a different geometrythan the schematic examples shown in FIG. 5. Regardless of theconfiguration and/or number of ports, the ports are collectively adaptedto deliver fluid for passage through the adsorbent region of the bed andto collect fluid that passes through the adsorbent region. As discussed,the ports may selectively, such as depending upon the particularimplementation of the PSA assembly and/or stage in the PSA cycle, beused as an input port or an output port. For the purpose of providing agraphical example, FIG. 6 illustrates a bed 100 in which the adsorbentregion extends along the entire length of the bed, i.e., between theopposed ports or other end regions of the bed. In FIG. 7, bed 100includes an adsorbent region 114 that includes discontinuous subregions120.

During use of an adsorbent bed, such as bed 100, to adsorb impuritygases (namely the gases with greater affinity for being adsorbed by theadsorbent), a mass transfer zone will be defined in the adsorbentregion. More particularly, adsorbents have a certain adsorptioncapacity, which is defined at least in part by the composition of themixed gas stream, the flow rate of the mixed gas stream, the operatingtemperature and/or pressure at which the adsorbent is exposed to themixed gas stream, any adsorbed gases that have not been previouslydesorbed from the adsorbent, etc. As the mixed gas stream is deliveredto the adsorbent region of a bed, the adsorbent at the end portion ofthe adsorbent region proximate the mixed gas delivery port will removeimpurities from the mixed gas stream. Generally, these impurities willbe adsorbed within a subset of the adsorbent region, and the remainingportion of the adsorbent region will have only minimal, if any, adsorbedimpurity gases. This is somewhat schematically illustrated in FIG. 8, inwhich adsorbent region 114 is shown including a mass transfer zone, orregion, 130.

As the adsorbent in the initial mass transfer zone continues to adsorbimpurities, it will near or even reach its capacity for adsorbing theseimpurities. As this occurs, the mass transfer zone will move toward theopposite end of the adsorbent region. More particularly, as the flow ofimpurity gases exceeds the capacity of a particular portion of theadsorbent region (i.e., a particular mass transfer zone) to adsorb thesegases, the gases will flow beyond that region and into the adjoiningportion of the adsorbent region, where they will be adsorbed by theadsorbent in that portion, effectively expanding and/or moving the masstransfer zone generally toward the opposite end of the bed.

This description is somewhat simplified in that the mass transfer zoneoften does not define uniform beginning and ending boundaries along theadsorbent region, especially when the mixed gas stream contains morethan one gas that is adsorbed by the adsorbent. Similarly, these gasesmay have different affinities for being adsorbed and therefore may evencompete with each other for adsorbent sites. However, a substantialportion (such as at least 70% or more) of the adsorption will tend tooccur in a relatively localized portion of the adsorbent region, withthis portion, or zone, tending to migrate from the feed end to theproduct end of the adsorbent region during use of the bed. This isschematically illustrated in FIG. 9, in which mass transfer zone 130 isshown moved toward port 118′ relative to its position in FIG. 8.Accordingly, the adsorbent 112′ in portion 114′ of the adsorbent regionwill have a substantially reduced capacity, if any, to adsorb additionalimpurities. Described in other terms, adsorbent 112′ may be described asbeing substantially, if not completely, saturated with adsorbed gases.In FIGS. 8 and 9, the feed and product ends of the adsorbent region aregenerally indicated at 124 and 126 respectively, and generally refer tothe portions of the adsorbent region that are proximate, or closest to,the mixed gas delivery port and the product port of the bed.

During use of the PSA assembly, the mass transfer zone will tend tomigrate toward and away from ends 124 and 126 of the adsorbent region.More specifically, and as discussed, PSA is a cyclic process thatinvolves repeated changes in pressure and flow direction. The followingdiscussion will describe the PSA cycle with reference to how steps inthe cycle tend to affect the mass transfer zone (and/or the distributionof adsorbed gases through the adsorbent region). It should be understoodthat the size, or length, of the mass transfer zone will tend to varyduring use of the PSA assembly, and therefore tends not to be of a fixeddimension.

At the beginning of a PSA cycle, the bed is pressurized and the mixedgas stream flows under pressure through the adsorbent region. Duringthis adsorption step, impurities (i.e., the other gases) are adsorbed bythe adsorbent(s) in the adsorbent region. As these impurities areadsorbed, the mass transfer zone tends to move toward the distal, orproduct, end of the adsorbent region as initial portions of theadsorbent region become more and more saturated with adsorbed gas. Whenthe adsorption step is completed, the flow of mixed gas stream 74 to theadsorbent bed and the flow of purified hydrogen gas (at least a portionof which will form product hydrogen stream 42) are stopped. While notrequired, the bed may then undergo one or more equalization steps inwhich the bed is fluidly interconnected with one or more other beds inthe PSA assembly to decrease the pressure and hydrogen gas present inthe bed and to charge the receiving bed(s) with pressure and hydrogengas. Gas may be withdrawn from the pressurized bed from either, or bothof, the feed or the product ports. Drawing the gas from the product portwill tend to provide hydrogen gas of greater purity than gas drawn fromthe feed port. However, the decrease in pressure resulting from thisstep will tend to draw impurities in the direction at which the gas isremoved from the adsorbent bed. Accordingly, the mass transfer zone maybe described as being moved toward the end of the adsorbent bed closestto the port from which the gas is removed from the bed. Expressed indifferent terms, when the bed is again used to adsorb impurities fromthe mixed gas stream, the portion of the adsorbent region in which themajority of the impurities are adsorbed at a given time, i.e., the masstransfer zone, will tend to be moved toward the feed or product end ofthe adsorbent region depending upon the direction at which theequalization gas is withdrawn from the bed.

The bed is then depressurized, with this step typically drawing gas fromthe feed port because the gas stream will tend to have a higherconcentration of the other gases, which are desorbed from the adsorbentas the pressure in the bed is decreased. This exhaust stream may bereferred to as a byproduct, or impurity stream, 76, which, as previouslymentioned, may be used for a variety of applications, including as afuel stream for a burner or other heating assembly that combusts a fuelstream to produce a heated exhaust stream. As discussed,hydrogen-generation assembly 46 may include a heating assembly 71 thatis adapted to produce a heated exhaust stream to heat at least thehydrogen-producing region 70 of the fuel processing system. According toHenry's Law, the amount of adsorbed gases that are desorbed from theadsorbent is related to the partial pressure of the adsorbed gas presentin the adsorbent bed. Therefore, the depressurization step may include,be followed by, or at least partially overlap in time, with a purgestep, in which gas, typically at low pressure, is introduced into theadsorbent bed. This gas flows through the adsorbent region and draws thedesorbed gases away from the adsorbent region, with this removal of thedesorbed gases resulting in further desorption of gas from theadsorbent. As discussed, a suitable purge gas is purified hydrogen gas,such as previously produced by the PSA assembly. Typically, the purgestream flows from the product end to the feed end of the adsorbentregion to urge the impurities (and thus reposition the mass transferzone) toward the feed end of the adsorbent region. It is within thescope of the disclosure that the purge gas stream may form a portion ofthe byproduct stream, may be used as a combustible fuel stream (such asfor heating assembly 71), and/or may be otherwise utilized in the PSA orother processes.

The illustrative example of a PSA cycle is now completed, and a newcycle is typically begun. For example, the purged adsorbent bed is thenrepressurized, such as by being a receiving bed for another adsorbentbed undergoing equalization, and optionally may be further pressurizedby purified hydrogen gas delivered thereto. By utilizing a plurality ofadsorbent beds, such as three or more, the PSA assembly may be adaptedto receive a continuous flow of mixed gas stream 74 and to produce acontinuous flow of purified hydrogen gas (i.e., a continuous flow ofproduct hydrogen stream 42). While not required, the time for theadsorption step, or stage, often represents one-third to two-thirds ofthe PSA cycle, such as representing approximately half of the time for aPSA cycle.

Regardless, it is important to stop the adsorption step before the masstransfer zone reaches the distal end (relative to the direction at whichthe mixed gas stream is delivered to the adsorbent region) of theadsorbent region. In other words, the flow of mixed gas stream 74 andthe removal of product hydrogen stream 42 preferably should be stoppedbefore the other gases that are desired to be removed from the hydrogengas are exhausted from the bed with the hydrogen gas. This is due to thefact that the adsorbent is saturated with adsorbed gases and thereforecan no longer effectively prevent these impurity gases from beingexhausted in what desirably is a purified hydrogen stream. Thiscontamination of the product hydrogen stream with impurity gases thatdesirably are removed by the PSA assembly may be referred to asbreakthrough, in that the impurities gases “break through” the adsorbentregion of the bed. Conventionally, carbon monoxide detectors have beenused to determine when the mass transfer zone is nearing or has reachedthe distal end of the adsorbent region and thereby is, or will, bepresent in the product hydrogen stream. Carbon monoxide detectors areused more commonly than detectors for other ones of the other gasespresent in the mixed gas stream because carbon monoxide can damage manyfuel cells when present in even a few parts per million (ppm).

As introduced in connection with FIG. 4, PSA assembly 73 includesdistribution assemblies 102 and 104 that selectively deliver and/orcollect mixed gas stream 74, product hydrogen stream 42, and byproductstream 76 to and from the plurality of adsorbent beds 100. Somewhat morespecifically, distribution assembly 102 is adapted, in some embodimentsvia one or more suitable distribution or collection manifolds, toselectively distribute the mixed gas stream to feed ends of theadsorbent beds 100, as indicated at 74′. Distribution assembly 102 isalso adapted to collect gas exhausted from the feed ends of theadsorbent beds, namely, the desorbed other gases, purge gas, and othergas that is not harvested to form product hydrogen stream 42. Theseexhaust streams are indicated at 76′ in FIG. 4 and collectively formbyproduct stream 76. As discussed, product hydrogen stream 42 is formedfrom the purified hydrogen gas streams produced in the adsorbent regionsof the adsorbent beds. It is within the scope of the present disclosurethat some of this gas may be used as a purge gas stream that isselectively delivered (such as via an appropriate distribution manifold)to the adsorbent beds during the purge and/or blowdown steps to promotethe desorption and removal of the adsorbed gases for the adsorbent. Thedesorbed gases, as well as the purge gas streams that are withdrawn fromthe adsorbent beds with the desorbed gases collectively may formbyproduct stream 76, which as discussed, may be used as a fuel streamfor heating assembly 71 or other device that is adapted to receive acombustible fuel stream, such as via combustible fuel stream supplysystem 140 (FIG. 2).

An illustrative and non-exclusive example of a fuel stream supply system140 is shown schematically in FIG. 10. Fuel stream supply system 140includes a delivery assembly, generally indicated at 142, that isadapted to receive and collect various combustible fuel streams, and toselectively deliver one or more fuel streams 92 having a combined fuelvalue at least as great as a corresponding, predetermined thresholdvalue to heating assembly 71. In the example shown in FIG. 10, deliveryassembly 142 is adapted to receive a portion of byproduct stream 76 fromthe PSA assembly 73, as well as a portion of mixed gas stream 74 fromthe hydrogen-producing region 70 prior to its delivery to the PSAassembly. Delivery assembly 142 optionally may receive other fuelstreams, which are represented generally at 150. Examples of suchoptional fuel streams include one or more other combustible streams fromother sources within hydrogen-generation assembly 46 or energy-producingsystem 22, such as portions of one or more of the product hydrogenstream produced by the PSA assembly, a fuel supply stream from thefeedstock delivery system, the anode exhaust stream from a fuel cell,and so forth, as well as fuel streams from storage tanks and othersources.

Although not required to all embodiments, delivery assembly 142 is shownto include a reservoir assembly 144, which further includes a reservoir1 46, which is adapted to receive and store at least some of the portionof the byproduct stream 76 that is directed from the PSA assembly to thefuel stream supply system 140. Of course, a reservoir assembly mayinclude any number of reservoirs 146 suitable to store one or morecombustible fuel streams for reuse as all or part of a fuel stream 92.In some embodiments, a reservoir 146 may be adapted to store a portionof any number of different fuel and fluid streams for reuse, orembodiments optionally may include additional reservoirs 146 for storageand reuse of other combustible fuels, and/or multiple reservoirs forstorage and reuse of one or more combustible fuels, as desired. Forexample, FIG. 10 schematically illustrates that a portion of the mixedgas stream 74 that is directed from the hydrogen-producing region 70 tothe fuel stream supply system 40, and/or a portion of one or more othergas streams 150 that are directed to the fuel stream supply system 140,may be stored for reuse in one or more reservoirs 146 of reservoirassembly 144, which may be different from, or the same as, thereservoir(s) 146 to which a portion of the byproduct stream is directed.

Although also not required to all embodiments, delivery assembly 142 isshown to include a collection assembly 152, which may function tocollect one or more streams and distribute fuel stream(s) 92 to theheating assembly. Thus, although collection assembly 152 is onlyschematically illustrated in FIG. 10, it may include any suitablestructure to selectively establish, distribute, restrict, regulate,meter, prevent, and/or collect flow of one or more of the fuel streamsshown, combine one or more streams, and deliver one or more streams 92to the heating assembly. Illustrative examples of such suitablestructures include one or more manifolds, such as collection anddistribution manifolds respectively adapted to collect one or more ofthe various streams, and deliver one or more fuel streams 92. In animplemented embodiment of fuel stream supply system 140, any suitablenumber, structure and construction of manifolds and fluid conduits forthe fluid streams discussed herein may be utilized.

The delivery assembly 142 in FIG. 10 is schematically illustrated toinclude several flow-regulating devices, indicated generally at 170,which may function to direct or otherwise regulate the flow of a fuelstream toward the reservoir assembly 144 and/or toward the collectionassembly 152 (if present) or directly to the heating assembly 71,individually or in combination with other fuel streams. Deliveryassembly 142 is also schematically shown to include sensors 172, whichmay function to measure fuel values of the various incoming fuel andfluid streams. In implemented embodiments, any suitable number and typeof valves or other flow-regulating devices 170, and/or sensors or otherproperty detectors 172, may be utilized. Examples of sensors andproperty detectors 172 include flow meters, pressure sensors,temperature sensors, composition detectors (such as carbon monoxide orother detectors, to detect the concentration, if any, of a targetmolecule or compound in a fluid or fuel stream), and so forth. Examplesof flow-regulating devices 170 include check valves, proportioning orother solenoid valves, pressure relief valves, variable orifice valves,fixed orifices, and so forth. One or more of such valves, sensors, andlike devices may be adapted to monitor the fuel value of the variousfuel and fluid streams, by detecting the combustible gas content of astream, its flow rate, chemical composition, and so forth, and may bepositioned as appropriate within fuel stream supply system 140. Forexample, FIG. 10 shows a sensor 172 disposed along each of redirectedmixed gas stream 74, byproduct stream 76, and gas stream(s) 150, forexample to monitor the fuel value of each fuel stream, upstream offlow-regulating devices 170, which may direct all or a portion of eachstream toward reservoir assembly 144. However, sensors 172 may bepositioned elsewhere, or may be incorporated into the various otherstructural components shown (for example, within hydrogen-producingregion 70 and/or PSA assembly 73, collection assembly 152, and soforth). Such valves, sensors, and like devices may thus be disposed asdesired within and throughout the hydrogen-generation assembly 46.Optionally, one or more other sections of the hydrogen-generationassembly may include flow-regulating devices 170 and sensors 172, forexample to monitor the fuel value of various fuel and fluid streams. Forexample, PSA assembly 73 may be adapted to monitor the fuel value of thebyproduct stream 76 produced by, and/or exhausted from, the adsorbentbeds of the PSA assembly.

While not required, it is within the scope of the present disclosurethat the fuel stream supply system may include, be associated with,and/or be in communication with a controller that is adapted to controlthe operation of at least portions of the PSA assembly and/or anassociated hydrogen-generation assembly and/or fuel cell system. Acontroller is schematically illustrated in FIGS. 2 and 10 and generallyindicated at 200. Controller 200 may communicate with at least theflow-regulating devices 170 and/or property detectors 172 via anysuitable wired and/or wireless communication linkage, as schematicallyillustrated in FIG. 10 at 202. This communication may include one- ortwo-way communication and may include such communication signals asinputs and/or outputs corresponding to measured or computed values,command signals, status information, user inputs, values to be stored,threshold values, etc. As illustrative, non-exclusive examples,controller 200 may include one or more analog or digital circuits, logicunits or processors for operating programs stored as software in memory,one or more discrete units in communication with each other, etc.Controller 200 may also regulate or control other portions of thehydrogen-generation assembly or fuel cell system and/or may be incommunication with other controllers adapted to control the operation ofthe hydrogen-generation assembly and/or fuel cell system. Controller 200is illustrated in both FIGS. 2 and 10 as being implemented as separatecomponents or controllers, but it may also be implemented as a discreteunit. Such separate controllers, then, can communicate with each otherand/or with other controllers present in system 22 and/or assembly 46via any suitable communication linkages.

In the illustrated embodiments, fuel stream supply system 140 may beadapted, such as via controller(s) 200, flow-regulating devices 170and/or property detectors 172, to monitor the fuel value of one or morefuel streams directed to the fuel stream supply system to provide one ormore fuel streams 92 having a combined fuel value at least as great as acorresponding, predetermined threshold value. Fuel stream supply system140 may supply either the byproduct stream, when the byproduct streamfrom the PSA assembly 73 has a fuel value at least as great as apredetermined threshold fuel value, and/or an auxiliary stream, during areduced byproduct period (or otherwise) when the fuel value of thebyproduct stream is lower than the threshold fuel value. In the lattercase, the fuel stream 92 supplied by the fuel stream supply system mayinclude an auxiliary stream, exclusive of, or in addition to, thebyproduct stream or a portion thereof.

The auxiliary stream(s) supplied during a reduced byproduct period, orwhen otherwise desired, may be provided as one or more “slip streams,”or streams that are directed, via the fuel stream supply system, to theheating assembly directly from the source of the stream (e.g., mixed gasstream 74 from hydrogen-producing region 70), as stored streams directedfrom the reservoir assembly to the heating assembly (e.g., a storedbyproduct stream from reservoir assembly 146), or a combination of slipand stored streams. The auxiliary stream(s) may be delivered via one ormore valves and other flow-regulating devices 170 that may be opened andclosed responsive to control signals. In some embodiments, the controlsignals may be generated responsive to the monitored fuel value of afuel stream, such as in programmed intervals that correlate with the PSAassembly's cycles, or otherwise as suitable to ensure a continuous flowof combustible fuel to the heating assembly that is sufficient, whencombusted, to produce a heated exhaust stream to maintain the hydrogenproducing region within a desired temperature range. In a somewhatsimplified example, the fuel stream supply system may be configured toautomatically supply an auxiliary stream consisting of a slip stream ofreformate from the hydrogen-producing region when the PSA assemblycycles through an equalization step. However, this example is onlyillustrative of several possible methods that may be practiced using theconcepts and components described herein.

Any suitable method or mechanism may be utilized for supplying one ormore fuel streams 92 (which may include one or more auxiliary streams)to the heating assembly. An illustrative, non-exclusive example is theuse of controller 200 to selectively actuate suitable flow-regulatingvalves to produce the desired stream composition, responsive to the fuelvalue of various available fuel streams. As discussed, any suitable typeand number of valves and sensors may be used, and it is within the scopeof the present disclosure that the valves, sensors, and assemblies thatregulate the flow of gas that will form stream(s) 92 may be selectivelyused, such as responsive to control signals from a controller.

Controller 200 may operate in conjunction with flow-regulating devices170 and sensors 172 to determine periods during which at least a portionof one or more fuel or fluid streams directed to the fuel stream supplysystem 140 are selectively directed to the reservoir assembly instead ofto the heating assembly. For example, if a byproduct stream from the PSAassembly has at least a predetermined threshold fuel value, or has afuel value greater than the predetermined threshold fuel value, thebyproduct stream or a portion thereof may be directed or diverted to thereservoir assembly for storage and later reuse as an auxiliary fuelstream, such as during a reduced byproduct period.

As mentioned briefly above, during such a period, the auxiliary fuelstream may consist of one or more streams, illustrative andnon-exclusive examples of which include the following:

-   -   solely the stored byproduct stream,    -   at least a portion of the stored byproduct stream together with        at least a portion of the byproduct stream discharged from the        PSA assembly,    -   at least a portion of the stored byproduct stream together with        at least a portion of the mixed gas stream redirected to the        fuel stream supply system prior to delivery to the PSA assembly,    -   at least a portion of the stored byproduct stream together with        at least a portion of the redirected mixed gas stream stored in        the reservoir assembly,    -   solely the redirected mixed gas stream, and    -   at least a portion of the redirected mixed gas stream together        with at least a portion of the byproduct stream discharged from        the PSA assembly.

This list is not exhaustive, because many variations and combinations ofthe aforementioned combustible fuel streams, individually, collectively,and/or together with other available and/or stored combustible fuelstreams, are available and considered to be within the scope of thisdisclosure.

As an illustrative and non-exclusive example of the operation of fuelstream supply system 140, during an equalization step of the PSAassembly, a stream 76′ may have a low flow rate and/or a low fuel value.As a result, the heating assembly may not be able to maintain a pilotlight or combustion flame without requiring a flow of fuel other thanbyproduct stream 76. Similarly, when the flow rate and/or fuel value ofstream 76 is low, the heated exhaust stream may not be able to heat theassociated structure, such as hydrogen-producing region 70, to a desiredtemperature or range of temperatures. However, the fuel stream supplysystem may be adapted to selectively supply, when a byproduct streamhaving at least a predetermined threshold fuel value is not dischargedfrom the PSA assembly, an auxiliary fuel stream to the heating assembly,such that the one or more streams supplied to the heating assembly havea combined combustion fuel value at least as great as the corresponding,predetermined threshold value.

In some embodiments, the collective threshold fuel value of the fuelstream(s) may produce a heated exhaust stream adapted to maintain thehydrogen-producing region of the fuel processing system at a desiredtemperature and/or within a desired temperature range, such as thosediscussed previously. For example, the heated exhaust stream may beadapted to maintain the hydrogen-producing region, which in someembodiments may be referred to as a reforming region, of thehydrogen-generation assembly at a relatively constant temperature.Illustrative, non-exclusive examples include a temperature in the rangeof 375-425° C., 400-425° C. and/or 400-450° C. for methanol or similarcarbon-containing feedstocks and a temperature in the range of 750-850°C., 775-825° C., 800-850° C., and/or 800-825° C. for natural gas,propane and similar carbon-containing feedstocks.

Using the subject matter discussed above as embodied in ahydrogen-generation assembly 46 that includes a fuel stream supplysystem 140, an illustrative and non-exclusive example of a method ofsupplying one or more fuel streams having at least a combined thresholdcombustion fuel value to a heating assembly adapted to receive andcombust such a combustion stream, and for producing a heated exhauststream therefrom, may include producing a mixed gas stream containinghydrogen gas, as a majority component, and other gases, in a heatedhydrogen-producing region of a fuel processing system. At least aportion of the mixed gas stream may then be delivered to a PSA assembly,followed by separating the mixed gas stream delivered to the PSAassembly into streams forming a product stream containing a greaterconcentration of hydrogen gas than the mixed gas stream and a byproductstream containing a substantial portion of the other gases, and cyclingthe PSA assembly through at least one reduced byproduct period duringwhich the combustion fuel value of the byproduct stream from thepressure swing adsorption assembly is lower than a predetermined,corresponding threshold value. The method may then include selectivelysupplying the byproduct stream to the heating assembly, such as duringperiods in which the byproduct stream has a fuel value at least as greatas the predetermined threshold value, and/or selectively supplying anauxiliary fuel stream to the heating assembly during the at least onereduced byproduct period. The method may then include combusting the oneor more streams supplied to the heating assembly, and heating at leastthe hydrogen-producing region with the heated exhaust stream to maintainthe hydrogen-producing region within a predetermined hydrogen-producingtemperature range.

As discussed above, in such a method, separating the mixed gas streamdelivered to the PSA assembly may include adsorbing the other gases fromthe mixed gas stream to produce the product stream, and depressurizingand purging the adsorbent bed to desorb the other gases therefrom andthereby produce the byproduct stream. The reduced byproduct period mayinclude an equalization step of the PSA assembly during which there isno flow of byproduct stream from the PSA assembly to the heatingassembly. Instead, the byproduct stream is redirected within the PSAassembly.

Also, in such a method, an auxiliary fuel stream supplied to the heatingassembly during the at least one reduced byproduct period may includeone or more combustible fuel streams discussed above, which may beregulated in some embodiments to use only an amount of an auxiliarystream sufficient, when combined with the byproduct stream, that theresulting supplied streams have a combined combustion fuel value atleast as great as the corresponding, predetermined threshold value. Theregulation may be based, at least in part, on the expected or actualfuel value of the byproduct stream, and may be performed, for example,by one or more controllers 200 via any suitable combination offlow-regulating devices 170. This regulation may additionally oralternatively be based, at least in part, on the current, or nextsequential, stage of the PSA cycle.

In some methods that include supplying a byproduct stream to the heatingassembly and supplying an auxiliary fuel stream to the heating assembly,such as methods that include alternating between supplying a byproductstream and an auxiliary stream, the former may at least partiallyoverlap in time with the latter, such as to ensure that a continuousflow of combustible fuel having a combined fuel value at least as greatas the predetermined threshold fuel value is supplied to the heatingassembly.

In embodiments in which a byproduct stream is discharged onlyintermittently from a PSA assembly, an illustrative and non-exclusiveexample of a method of intermittently supplying an auxiliary fuel streamhaving at least a threshold combustion fuel value to a heating assemblyadapted to receive such a fuel stream and to produce a heated exhauststream therefrom, may include producing a mixed gas stream containinghydrogen gas, as a majority component, and other gases, in a heatedhydrogen-producing region of a fuel processing system, and delivering atleast a portion of the mixed gas stream to the PSA assembly. The methodmay then include separating the mixed gas stream delivered to the PSAassembly into a product stream containing a greater concentration ofhydrogen gas than the mixed gas stream and a byproduct stream containinga substantial portion of the other gases, and intermittently dischargingfrom the PSA assembly the byproduct stream and delivering at least aportion of the byproduct stream discharged from the PSA assembly to theheating assembly. When a byproduct stream is not discharged from the PSAassembly, the method may include one or more of redirecting to theheating assembly a portion of the mixed gas stream that is not deliveredto the pressure swing adsorption assembly, and selectively storing atleast a portion of the byproduct stream discharged from the pressureswing adsorption assembly and directing to the heating assembly aportion of the stored byproduct stream. The method may then includecombusting the one or more streams supplied to the heating assembly, andheating at least the hydrogen-producing region with the heated exhauststream to maintain the hydrogen-producing region within a predeterminedhydrogen-producing temperature range.

Illustrative, non-exclusive examples of implementations of the systemsand methods for providing one or more fuel streams having a combinedfuel value at least as great as a predetermined threshold fuel valuethat is sufficient, when combusted to produce a heated exhaust stream,to maintain a hydrogen-producing region within a desiredhydrogen-producing temperature range include, but are not limited to,one or more of the following implementations:

Supplying one or more fuel streams having at least a combined thresholdcombustion fuel value to a heating assembly adapted to receive andcombust such a combustion stream, and for producing a heated exhauststream therefrom;

Intermittently supplying an auxiliary fuel stream having at least athreshold combustion fuel value to a heating assembly adapted to receivesuch a fuel stream to produce a heated exhaust stream therefrom;

Producing a mixed gas stream containing hydrogen gas, as a majoritycomponent, and other gases, in a heated hydrogen-producing region of afuel processing system;

Delivering at least a portion of a mixed gas stream to a pressure swingadsorption assembly;

Separating a mixed gas stream delivered to a PSA assembly into streamsforming a product stream containing a greater concentration of hydrogengas than the mixed gas stream and a byproduct stream containing asubstantial portion of the other gases;

Adsorbing other gases from a mixed gas stream to produce a productstream and depressurizing and purging an adsorbent bed to desorb theother gases therefrom and thereby produce a byproduct stream;

Cycling through at least one reduced byproduct period during which thecombustion fuel value of a byproduct stream from a PSA assembly is lowerthan a predetermined, corresponding threshold value;

Cycling through at least one equalization step during which there is noflow of a byproduct stream from a PSA assembly to a heating assembly;

Redirecting a byproduct stream within a PSA assembly during anequalization step;

Intermittently discharging from a PSA assembly a byproduct stream anddelivering at least a portion of the byproduct stream discharged fromthe PSA assembly to a heating assembly;

Selectively supplying a byproduct stream to a heating assembly, andselectively supplying an auxiliary fuel stream to the heating assemblyduring at least a reduced byproduct period;

Supplying a portion of a mixed gas stream that is not delivered to thePSA assembly as an auxiliary fuel stream;

Supplying only the portion of a mixed gas stream that is not deliveredto the PSA assembly as an auxiliary fuel stream;

Selectively storing at least a portion of a byproduct stream from a PSAassembly for reuse, and supplying at least a portion of the storedbyproduct stream as an auxiliary fuel stream;

Selectively storing at least a portion of a product stream from a PSAassembly for reuse, and supplying at least a portion of the storedproduct stream as an auxiliary fuel stream;

Regulating an auxiliary fuel stream supplied to a heating assembly byusing an amount of a, auxiliary fuel stream that is sufficient, whencombined with a byproduct stream, that the resulting supplied streamshave a combined combustion fuel value at least as great as thecorresponding, predetermined threshold value;

Monitoring the combustion fuel value of a byproduct stream;

Regulating the auxiliary fuel stream supplied to the heating assemblybased at least in part on the combustion fuel value of a byproductstream;

Supplying a byproduct stream to a heating assembly at least partiallyoverlapping in time with selectively supplying an auxiliary fuel streamto the heating assembly;

Supplying an auxiliary fuel stream to a heating assembly when abyproduct stream is not discharged from a PSA assembly, by one or moreof redirecting to a heating assembly a portion of a mixed gas streamthat is not delivered to the PSA assembly, and selectively storing atleast a portion of the byproduct stream discharged from the PSA assemblyand directing to the heating assembly a portion of the stored byproductstream;

Combusting one or more streams supplied to a heating assembly;

Heating at least a hydrogen-producing region with a heated exhauststream to maintain the hydrogen-producing region within a predeterminedhydrogen-producing temperature range;

Any of the above systems or methods implemented with a PSA assemblyhaving a plurality of adsorbent beds adapted to receive a mixed gasstream that includes hydrogen gas as its majority component and which isproduced by a fuel processing system that includes at least onereforming region adapted to produce the mixed gas stream by steamreforming water and a carbon-containing feedstock, with at least thereforming region(s) of the fuel processing system adapted to be heatedby a heating assembly, with the PSA assembly adapted to provide at leastone fuel stream to the heating assembly, and optionally in furthercombination with a fuel cell stack adapted to receive at least a portionof the purified hydrogen gas produced by the PSA assembly;

Methods for implementing the processes of any of the above systemsand/or use of any of the above systems; and/or

A control system adapted to control the operation of a PSA assemblyand/or an associated hydrogen-generation assembly to implement any ofthe above methods or control systems.

These implementations may be implemented in one or more of a PSAassembly; a PSA assembly adapted to purify hydrogen gas; a fuelprocessing system having a hydrogen-producing region adapted to receivea feed stream and to produce a mixed gas stream containing hydrogen gasand other gases therefrom, wherein hydrogen gas forms a majoritycomponent of the mixed gas stream; a heating assembly adapted to receiveand combust one or more streams having a combined combustion fuel valueat least as great as a corresponding, predetermined threshold andthereby produce a heated exhaust stream sufficient to heat and maintainat least a hydrogen-producing region within a predetermined temperaturerange for producing a mixed gas stream; a PSA assembly adapted toseparate at least a portion of a mixed gas stream into streams forming aproduct stream and a byproduct stream, the product stream containing atleast substantially pure hydrogen gas and having a reduced concentrationof the other gases than the mixed gas stream, and the byproduct streamcontaining at least a substantial portion of the other gases; a PSAassembly adapted to intermittently discharge a byproduct stream havingat least a predetermined threshold fuel value; a PSA assembly with aplurality of adsorbent beds, each bed including an adsorbent regioncontaining adsorbent adapted to adsorb at least one of the other gases;a PSA assembly adapted to cycle through an equalization step in which atleast two adsorbent beds are fluidly interconnected for gas flow betweenthe beds; a PSA assembly adapted such that a byproduct stream having atleast a predetermined threshold fuel value is not discharged from thePSA assembly during an equalization step; a combustion fuel streamsupply system adapted to selectively supply a byproduct stream to aheating assembly and to also selectively supply, when a byproduct streamhaving at least a predetermined threshold fuel value is not dischargedfrom a PSA assembly, an auxiliary fuel stream to the heating assembly,such that the one or more streams supplied to the heating assembly havea combined combustion fuel value at least as great as the corresponding,predetermined threshold value; a reservoir assembly adapted to receiveand store at least a portion of a byproduct stream having at least apredetermined threshold fuel value discharged from a PSA assembly; acombustion fuel stream supply system adapted to selectively direct atleast a portion of a byproduct stream having at least a predeterminedthreshold fuel value discharged from a PSA assembly to a reservoirassembly and to selectively use at least a portion of the storedbyproduct stream when supplying an auxiliary fuel stream; a combustionfuel stream supply system adapted to selectively redirect at least aportion of a mixed gas stream produced by a fuel processing system priorto delivery to a PSA assembly, and to use at least a portion of theredirected mixed gas stream when supplying an auxiliary fuel stream; acombustion fuel stream supply system adapted to selectively redirect atleast a portion of a mixed gas stream produced by a fuel processingsystem prior to delivery to a PSA assembly, and to use at least aportion of the redirected mixed gas stream when supplying an auxiliaryfuel stream; and a combustion fuel stream supply system adapted tomonitor the combustion fuel value of one or more of a byproduct stream,a mixed gas stream delivered to a PSA assembly, and an auxiliary stream.

Although discussed herein in the context of a PSA assembly for purifyinghydrogen gas, it is within the scope of the present disclosure that thePSA assemblies disclosed herein, as well as the methods of operating thesame, may be used in other applications, such as to purify other mixedgas streams in fuel cell or other systems and/or to heat structure otherthan a hydrogen-producing region of a fuel processing system.

INDUSTRIAL APPLICABILITY

The pressure swing adsorption assemblies, combustion fuel stream supplysystems, and hydrogen-generation and/or fuel cell systems including thesame are applicable in the gas generation and fuel cell fields,including such fields in which hydrogen gas is generated, purified,and/or consumed to produce an electric current.

It is believed that the disclosure set forth above encompasses multipledistinct inventions with independent utility. While each of theseinventions has been disclosed in its preferred form, the specificembodiments thereof as disclosed and illustrated herein are not to beconsidered in a limiting sense as numerous variations are possible. Thesubject matter of the inventions includes all novel and non-obviouscombinations and subcombinations of the various elements, features,functions and/or properties disclosed herein. Similarly, where theclaims recite “a” or “a first” element or the equivalent thereof, suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.

It is believed that the following claims particularly point out certaincombinations and subcombinations that are directed to one of thedisclosed inventions and are novel and non-obvious. Inventions embodiedin other combinations and subcombinations of features, functions,elements and/or properties may be claimed through amendment of thepresent claims or presentation of new claims in this or a relatedapplication. Such amended or new claims, whether they are directed to adifferent invention or directed to the same invention, whetherdifferent, broader, narrower, or equal in scope to the original claims,are also regarded as included within the subject matter of theinventions of the present disclosure.

1. A method for supplying one or more fuel streams having at least acombined threshold combustion fuel value to a heating assembly adaptedto receive and combust such a combustion stream, and for producing aheated exhaust stream therefrom, the method comprising: supplying a feedstream to a heated hydrogen-producing region of a fuel processingsystem; producing a mixed gas stream containing hydrogen gas, as amajority component, and other gases, in the heated hydrogen-producingregion of the fuel processing system; delivering at least a portion ofthe mixed gas stream to a pressure swing adsorption assembly containingat least an adsorbent bed; separating the mixed gas stream delivered tothe pressure swing adsorption assembly into streams forming a productstream containing a greater concentration of hydrogen gas than the mixedgas stream and a byproduct stream containing a substantial portion ofthe other gases, wherein the separating includes cycling through atleast one reduced byproduct period during which the combustion fuelvalue of the byproduct stream from the pressure swing adsorptionassembly is lower than a corresponding, predetermined threshold value,wherein the cycling is performed as part of the separating; selectivelysupplying the byproduct stream to the heating assembly as a fuel stream;selectively supplying an auxiliary fuel stream to the heating assemblyduring the at least one reduced byproduct period; combusting the one ormore fuel streams supplied to the heating assembly; and heating at leastthe hydrogen-producing region with the heated exhaust stream to maintainthe hydrogen-producing region within a predetermined hydrogen-producingtemperature range.
 2. The method of claim 1, wherein the separatingincludes adsorbing the other gases from the mixed gas stream to producethe product stream and depressurizing and purging the adsorbent bed todesorb the other gases therefrom and thereby produce the byproductstream.
 3. The method of claim 1, wherein the at least one reducedbyproduct period includes an equalization step during which there is noflow of byproduct stream from the pressure swing adsorption assembly tothe heating assembly.
 4. The method of claim 3, wherein the byproductstream is redirected within the pressure swing adsorption assemblyduring the equalization step.
 5. The method of claim 1, wherein theselectively supplying an auxiliary fuel stream includes supplying aportion of the mixed gas stream that is not delivered to the pressureswing adsorption assembly.
 6. The method of claim 5, wherein theselectively supplying an auxiliary fuel stream includes supplying onlythe portion of the mixed gas stream that is not delivered to thepressure swing adsorption assembly.
 7. The method of claim 5, furthercomprising selectively storing at least a portion of the byproductstream from the pressure swing adsorption assembly for reuse, andwherein the selectively supplying an auxiliary fuel stream furtherincludes supplying at least a portion of the stored byproduct stream. 8.The method of claim 1, further comprising selectively storing at least aportion of the byproduct stream from the pressure swing adsorptionassembly for reuse, and wherein the selectively supplying an auxiliaryfuel stream includes at least a portion of the stored byproduct stream.9. The method of claim 8, wherein the selectively supplying an auxiliaryfuel stream includes supplying only the stored byproduct stream.
 10. Themethod of claim 8, wherein the selectively supplying an auxiliary fuelstream further includes supplying at least a portion of the mixed gasstream that is not delivered to the pressure swing adsorption assembly.11. The method of claim 1, wherein the selectively supplying anauxiliary fuel stream further includes regulating the auxiliary fuelstream supplied by using an amount of the auxiliary fuel streamsufficient, when combined with the byproduct stream, that the resultingsupplied streams have a combined combustion fuel value at least as greatas the corresponding, predetermined threshold value.
 12. The method ofclaim 11, further including monitoring the combustion fuel value of thebyproduct stream, and wherein regulating the auxiliary fuel streamsupplied is based at least in part on the combustion fuel value of thebyproduct stream.
 13. The method of claim 1, wherein the selectivelysupplying the byproduct stream to the heating assembly at leastpartially overlaps in time with selectively supplying an auxiliary fuelstream to the heating assembly.
 14. The method of claim 1, furthercomprising selectively storing at least a portion of the product streamfrom the pressure swing adsorption assembly for reuse, and wherein theselectively supplying an auxiliary fuel stream includes at least aportion of the stored product stream.
 15. The method of claim 1, whereinthe reduced byproduct period includes an equalization step of a pressureswing adsorption cycle of the pressure swing adsorption assembly, andfurther wherein, during the equalization step, the method furtherincludes redirecting at least a portion of the byproduct stream withinthe pressure swing adsorption assembly.
 16. The method of claim 15,wherein the redirecting includes ceasing a flow of the byproduct streamfrom the pressure swing adsorption assembly.
 17. The method of claim 1,wherein the cycling includes periodically cycling through the reducedbyproduct period, wherein the periodically cycling includesintermittently discharging the byproduct stream from the pressure swingadsorption assembly.
 18. The method of claim 1, wherein the cycling isnot associated with a start-up operation of the pressure swingadsorption assembly.
 19. The method of claim 1, wherein the cyclingincludes cycling through a plurality of reduced byproduct periods aspart of a pressure swing adsorption cycle.
 20. A method forintermittently supplying an auxiliary fuel stream having at least athreshold combustion fuel value to a heating assembly adapted to receivesuch a fuel stream to produce a heated exhaust stream therefrom, themethod comprising: supplying a mixed gas stream to a heatedhydrogen-producing region of a fuel processing system; producing a mixedgas stream containing hydrogen gas, as a majority component, and othergases, in the heated hydrogen-producing region of the fuel processingsystem; delivering at least a portion of the mixed gas stream to apressure swing adsorption assembly; separating the mixed gas streamdelivered to the pressure swing adsorption assembly into a productstream containing a greater concentration of hydrogen gas than the mixedgas stream and a byproduct stream containing a substantial portion ofthe other gases, wherein the separating includes intermittentlydischarging from the pressure swing adsorption assembly the byproductstream and delivering at least a portion of the byproduct streamdischarged from the pressure swing adsorption assembly to the heatingassembly, wherein the intermittently discharging is performed as part ofthe separating; supplying an auxiliary fuel stream to the heatingassembly when the byproduct stream is not discharged, by one or more of:redirecting to the heating assembly a portion of the mixed gas streamthat is not delivered to the pressure swing adsorption assembly; andselectively storing at least a portion of the byproduct streamdischarged from the pressure swing adsorption assembly and directing tothe heating assembly a portion of the stored byproduct stream;generating the heated exhaust stream by combusting at least portions ofany of the byproduct stream and the auxiliary fuel stream delivered tothe heating assembly; and heating at least the hydrogen-producing regionwith the heated exhaust stream to maintain the hydrogen-producing regionwithin a predetermined hydrogen-producing temperature range.
 21. Themethod of claim 20, wherein the intermittently discharging includesequalizing pressure within at least a portion of the pressure swingadsorption assembly, and further wherein, during the equalizing, themethod further includes redirecting at least a portion of the byproductstream within the pressure swing adsorption assembly.
 22. The method ofclaim 21, wherein the redirecting includes ceasing a flow of thebyproduct stream from the pressure swing adsorption assembly.
 23. Themethod of claim 20, wherein the intermittently discharging includesperiodically cycling through the reduced byproduct period as part of apressure swing adsorption cycle.
 24. The method of claim 20, wherein theintermittently discharging is not associated with a start-up operationof the pressure swing adsorption assembly.